The invention concerns a mechanically-controlled power transmission device, in particular for automotive vehicle applications, such as control of braking pressure in a brake or the rapid correction of a hydropneumatic suspension.
Among the numerous present-day solutions to the problem of mechanically-controlled power transmission, hydraulic systems such as hydraulic servo valves appear the best suited for incorporation into vehicles or other motorized equipment, since they are inexpensive and can be easily and quickly adapted to new technical or economic requirements.
A hydraulic servo valve can be defined as the interface between an electric or electronic device supplying a control signal, and a hydraulic device designed to provide a response as a function of this electrical signal.
The characteristics required of a servo-valve are as follows:
It must be usable for all automatic control applications, including:
automatic pressure control, for example in a brakecontrol mechanism,
automatic movement control, for example of the position of a hydraulic jack,
automatic flow control, for example in order to make rapid correction in the hydropneumatic suspension of a vehicle.
The servo-valve must possess a high transmission band, so as to allow the rapid, stable response of the automatic control function, independently of the requisite hydraulic flow rate.
The servo valve must be compatible with the conditions governing automotive operation, by providing:
a low cost price,
operation within a broad temperature range,
low level of sensitivity to impurities, thus requiring no major precautions for use and filtration of the hydraulic fluid,
low energy consumption,
a virtually nil hydraulic consumption under all circumstances,
lack of sensitivity to vibrations and acceleration.
A servo valve possessing all of these features is known, this valve comprising a rotary actuating element, such as a rotary electric motor of low inertia, controlled in position and connected by mechanical linkage means to a mechanical device such as a hydraulic distributor incorporating a linear valve, this motor being equipped with a return spring brasing it in its initial position.
A device of this kind is well suited for use in a vehicle, since the rotary electric motor is insensitive to vibrations and acceleration, which have no effect on its angular position. This is not the case in a linear motor, the metallic weight of which can be shifted because of the effect of inertia. Hydraulic distributors incorporating linear valves are currently in wide-spread use, in the automotive industry, since they are inexpensive, show little sensitivity to impurities, and since, because the very low weight of the valve, acceleration along its axis creates only very weak forces.
However, this conventionally-known device exhibits a number of problems related to the inevitable presence of clearances in the connection between the actuating element and the valve. The result is a degree of imprecision in the position of the valve and premature wear of the parts. Moreover, in the event of breakage of the mechanical linkages, the hydraulic valve may either remain in its position, which is not necessarily the position corresponding to the greatest driving safety in the event of breakdown of the hydraulic system, or it may shift uncontrollably.
Accordingly, the invention is intended to solve these problems by proposing a mechanically-controlled power-transmission device comprising an actuating element, or rotary motor, and linkage means connecting this actuating element to a mechanical device such as a hydraulic valve, in order to transmit linear motion to this valve, this device being characterized by the fact that it comprises means for clearance adjustment and for return of the mechanical device into a predetermined safety position.
Other features of the device according to the invention include:
because the valve can establish or prevent connection between at least one user device and either one high-pressure source or exhaust, the predetermined safety position is a position in which linkage is created between said user device, on the one hand, and the high-pressure source or exhaust, on the other;
the clearance-adjustment and mechanical device-return means act directly on the valve;
the clearance-adjustment and mechanical device-return means comprise a spring or comparable mechanism which acts on the end of the valve;
said device further comprises means for ensuring the return motion of the motor into a predetermined neutral position;
said device also comprises additional return-motion means incorporated into the linkage mechanism;
the axis of rotation of the motor is perpendicular to the axis of the valve;
the linkage mechanism comprises a lever fastened to the rotor of the motor and of which one arm, located at a determinate distance from the axis of rotation of the latter, acts on a part fastened to the valve;
the lever comprises a first arm extending perpendicularly to the axis of rotation of the motor and of which one end is attached to the rotor at said axis, and a second arm constituting the aforementioned arm and extending perpendicularly to the first;
said part integral with the valve is in the shape of a clevis, and said arm has a barrel-shaped part acting on this clevis;
said arm is linked to the valve by means of a connecting rod whose two ends are jointed to the arm and the valve, respectively, by means of ball joints;
said device is configured in such a way that, in the central position of the valve, at least one of the following conditions is fulfilled:
the motor lies substantially in the middle of its course of travel,
the lever is perpendicular to the valve axis,
the axis of the valve is concurrent with the axis of the arm or of the ball joint of the lever;
the axis of rotation of the motor is collinear to the axis of the valve;
the linkage mechanism comprises at least one roller integral with the valve and whose axis is perpendicular to the valve, and which slides on a helical inclined surface provided in the wall of a cylindrical part driven by the motor in rotation a round its own axis , which is parallel, and preferably collinear, to the axis of the motor, and means for maintaining the axis of said roller in translational motion in a direction parallel to the axis of the valve;
said translational motion-maintenance means comprise at least one guide roller having the same axis as the first and also integral with the valve, this guide roller being able to roll in a groove parallel to the axis of the valve and cut in a stationary part;
the linkage mechanism comprises:
a first plate arranged perpendicularly to the axis of the motor and driven in rotation by the latter;
a second plate attached to the valve casing and positioned opposite and parallel to the first; and
at least one lever incorporating:
a first arm whose ends are jointed to each of the two plates; and
a second arm forming a non-null angle with the first and acting on the end of the valve;
said device comprises a return spring in the area of the plates;
the valve comprises a rod fitted with blocks which slide in a bore in a sleeve and which are capable of freeing or sealing radial holes connecting with said user device, the high-pressure source and the exhaust, at least one of the holes having a non-circular section and being configured so that his section increases gradually and uniformly as it is freed by the corresponding block when the valve moves;
said hole has a circular or similar section on one side and ends in a point on the opposite side;
the hole(s) end(s) in an annular groove provided on the outside of the valve sleeve and/or in an annular groove provided on the wall of the bore;
the bore has two orifices, each connecting with a user device, two orifices connecting with the exhaust, and one orifice connecting with the high-pressure source, the number and arrangement of the blocks being such that, when one user device is connected to the exhaust, the other is connected to the high-pressure source, and vice-versa.